1. Field of the Invention
The present invention generally relates to vibratory gyroscopes used to detect the angular velocity in various devices such as vibration detection in video cameras and still cameras, car navigation systems and vehicle attitude control. More particularly, the present invention is concerned with a tuning-fork type piezoelectric vibratory gyroscope equipped with a tune for, made of a piezoelectric substance such as a piezoelectric single crystal and piezoelectric ceramics.
2. Description of the Related Art
Various tuning-fork type vibratory gyroscopes are known, and a vibratory gyroscope which employs a piezoelectric single crystal such as LiTaO.sub.3 or LiNbO.sub.3 has recently been proposed.
FIGS. 1A and 1B show a conventional vibratory gyroscope having a piezoelectric single crystal. The gyroscope has a tuning fork (vibrator) 10, which has two arms 12 and 14 and a base portion 15 and is formed of a piezoelectric crystal. Drive electrodes 16, 18, 20 and 22 and detection electrodes 24, 26, 28, 30, 32 and 34 are provided on surfaces of the tuning fork 10, as shown in FIGS. 1A and 1B. A driving source OSC is connected between the drive electrodes 16 and 18 in order to cause a drive-side vibration. The drive electrodes 20 and 22 opposite the drive electrodes 16 and 18 are grounded. The detection electrodes 24, 26, 28, 30, 32 and 34 are connected as shown in FIGS. 1A and 1B so that two signals are output.
When the tuning fork 10 is driven, the two arms 12 and 14 start vibrating, as shown in the left side of FIG. 2. The vibration of the two arms 12 and 14 is called an in-plane vibration. If the gyroscope is rotated about the Z axis in the above state, a Coriolis force is generated in the Y-axis directions perpendicular in the X-axis directions, and the arms 12 and 14 are vibrated in the Y-axis directions with a magnitude proportional to the Coriolis force. The vibration caused in the Y-axis direction are called a surface-perpendicular vibration. The Coriolis force is proportional to the angular velocity, which can thus be detected by detecting an output signal proportional to the magnitude of the vibration caused in the Y-axis directions.
The tuning-fork type piezoelectric gyroscope shown in FIGS. 1A and 1B is disclosed in, for example, Japanese Laid-Open Patent Application No. 8-128830. This Application further discloses that the tuning fork shown in FIGS. 1A and 1B is attached to a supporting member so that the tuning fork and the supporting member are integrally vibrated due to the Coriolis force. The Application shows that, by changing the shape of the supporting member, the stiffness can be changed and the detection-side vibration can be sufficiently attenuated at an and portion of the supporting member.
The tuning-fork type vibratory gyroscope shown in FIGS. 1A and 1B has the following disadvantages. The above-mentioned Japanese Patent Application does not disclose any consideration of the relationship between the temperature range in which the gyroscope is used and the performance of the gyroscope. The inventors found that the temperature of the gyroscope and the performance thereof has a close relationship. More particularly, the vibration mode is changed at a certain temperature, and causes unwanted vibrations. In this case, the unwanted vibrations appear a leakage voltage in the detection signal, and the performance of the gyroscope is degraded.
Further, the Application discloses that the resonance frequency of the detection-side vibration can be changed by changing the shape of the supporting member to which the tuning fork is attached. However, the Application fails to disclose the relationship between the drive-side resonance and the detection-side resonance, particularly the relationship between the detection sensitivity and the frequency difference between the drive-side vibration and the detection-side vibration.
Furthermore, the Application discloses that the gyroscope and a wiring board, on which a detection circuit for processing the detection signals of the gyroscope is formed, are electrically connected together by wire bonding. However, the operationability of wire bonding is not good.